It is known in the art of firing pulse generators for static power converters to trigger a one-shot multivibrator at an instant corresponding to a desired fire angle upon selecting with a ring counter the next thyristor rectifier to be fired. The firing control circuit of the appropriate thyristor is selected by a distributor and the generated firing pulse is passed to the firing control circuit of the thyristor as selected by the distributor.
It is also known to generate an "extended" firing pulse lasting for the total conduction period, e.g., up to the point of natural commutation of the thyristor rectifier. See, for instance, Chapter 10 of B. R. Pelly "Thyristor Phase-Controlled Converters and Cycloconverters", published by John Wiley in 1971. Pelly also underlies in this book the importance of the leading edge in the ignition process and also mentions the usefulness of an extended pulse for reliable operation under all circumstances. A technique is mentioned by Pelly consisting in providing a "pseudo-extended" firing pulse (see page 274) formed with a train of shorter pulses instead of a continuous pulse, but Pelly also states that problems are encountered with such technique.
Pelly also describes end-stop control (see page 259) for limiting the excursions of the firing control range in the rectification and in the inversion portions of the conduction period. In Pelly further is to be found (see page 277) the technique of inhibiting the firing pulses by inhibiting the master oscillator generating "pseudo-extended" pulses instead of the ring distributor circuits.
More generally, Chapter 10 of the book by B. R. Pelly provides a general background against which to distinguish the present invention, and also discloses such prior art as can be used to support the description herein of a typical firing pulse generator to which the present invention is applicable. For the latter reason, Chapter 10 (namely from page 248 to page 277) of Brian R. Pelly, "Thyristor Phase-Controlled Converters and Cycloconverters" published in 1971 by John Wiley is hereby incorporated by reference.
An object of the present invention is to provide a firing pulse generator in which two kinds of pulses are successively applied to each selected thyristor rectifier, one pulse called a "hard pulse" being initiated for actually firing the rectifier, followed by a train of short pulses for refreshing the state of conduction throughout the desired conduction period.
Another object of the present invention is to provide a firing pulse generator for thyristors in which two kinds of pulses are successively applied to each selected thyristor, and in which provision is made for inhibition of either kind of pulses.